2013 Volume 64 Issue 1-2 Pages 25-49
Microgranular dark-colored enclaves from medium-grained porphyritic biotite granites in the Tanakami Granite pluton were studied petrographically, geochemically and mineralogically. Many of them are ball-like in form with a diameter of ~1~20~ cm. They consist mainly of fine-grained plagioclase, quartz, biotite and several accessory minerals together with porphyritic plagioclase (mainly) and quartz (subordinately). The maximum biotite content is ca. 27 % in mode analysis. The occurrence of alkali feldspar is limited to be as small patches seemingly replacing plagioclase interiors. Their occurrence, textures, bulk rock chemistry, REE patterns, mineral textures and its chemistry seem to be totally consistent with the idea that they are not a product of magma mixing but is a product of early-stage crystallization from the magma forming the medium-grained porphyritic biotite granites as the host rock. The MME often occurs with aplite-pegmatite facies (dykes), which suggests some common circumstances such as relatively rapid cooling conditions catalyzed by some volatile components.
